The present invention relates to a method of detecting discontinuities on elongated workpieces, in particular on tubes and bars, using ultrasound.
German patent publication DE 36 22 500 A1 discloses a process and apparatus for the detection of discontinuities on cylindrical tubes and bars. Discontinuities are detected by moving the test object past stationary transmission and receiving transducers, which detect tangentially circulating guided wave pulses in the test object, whereby the amplitudes of the sequentially received signals are processed in a computer by forming a quotient to determine defects. The received signals are synchronized for evaluation with burst signals of the same frequency, a suitable time period and start delay, and transmitted to a peak detector. The amplitudes are digitized and transmitted to a computer.
German patent publication DE 39 43 226 C2 discloses a process for the detection of discontinuities on elongated workpieces, in particular on tubes and bars, using ultrasonic inspection. In the disclosed process, the test object is moved without rotation in an axial direction past a stationary electrodynamic transducer. Clocked wave pulses which circulate tangentially in the test object and propagate in two circumferential directions are received at a receiving site which is shifted relative to the transmission site by one quarter of the wavelength of the confined waves. The location of reception and the excitation of the wave pulses propagating simultaneously in both circumferential directions of the test object is selected such that both uninterfered circulating waves destructively interfere at the site of the receiver. For each cycle, the reception signal and a burst signal which has a high pulse duty ratio and period selected to be less than one quarter of the revolution time of the wave pulses about the test object and a length that corresponds to the decay time of the unobstructed wave pulses, is transmitted to a peak detector. The output signal of the peak detector is digitized and transmitted to a computer.
Both these conventional process suffer shortcomings because very short discontinuities, e.g. a hole, or discontinuities in unfavorable location may not be detected due to a low signal level.
It would therefore be desirable and advantageous to provide an improved process of detecting discontinuities on elongated workpieces to obviate prior art shortcomings and to enable a detection of short defects in the workpiece.